There are many different screen sizes but most people now a days work in 1024 x 768,that means your site has to be a smaller then 1024 x 768 in order to make it fit perfectly. But you can never reach it on every PC, cause some people have more things on there screen then others. Witch leads to less space.
The only program that can automatically stretch to any screens resolution is Flash, but if your familiar with the program it can take a long time to make a website.
Personally i work in 800x600 in dreamweaver, by using a small resolution it will always fit on any screen. And because Dreamwaever uses frames, you can at extra frames to site that can not be seen on a small screen, but can be seen on a bigger resolution. Off course all your main bottoms or other important things have to be in the main screen.
If you make your background very big it can be seen in any resolution, as long as all the important things are in the center.
Hope this helps.
